1. Field of the Invention
This invention relates to a ceramic orthodontic bracket having a channel for facilitating removal of the bracket from a tooth.
2. Description of the Related Art
Orthodontic treatment involves movement of the teeth toward positions for correct occlusion. During treatment, tiny orthodontic appliances known as brackets are connected to the teeth, and an archwire is placed in a slot of each bracket. The archwire forms a track to guide movement of the teeth to orthodontically correct positions.
Orthodontic brackets are typically made of metal, ceramic or plastic. Metal brackets are widely used and are considered by many orthodontists to have mechanical properties that are satisfactory for moving the teeth to desired positions. Unfortunately, metal brackets are not aesthetic in the mouth and often lead to comments of a "metallic mouth appearance" that can be an embarrassment to the patient.
Orthodontic brackets that are made of a plastic material are generally considered more aesthetic than metal brackets. However, some plastic brackets are stained by certain food and beverages and turn an unsightly color after a period of time. Moreover, the plastic material may slowly creep in use such that the archwire slot widens and precise control of tooth movement is hindered.
Orthodontic brackets that are made of transparent or translucent ceramic materials overcome many of the problems associated with plastic brackets, since ceramic material is resistant to staining and does not deform by creep as in the case with plastic brackets. U.S. Pat. No. 4,954,080, assigned to the assignee of the present invention, describes a color-free ceramic bracket made of polycrystalline material with a translucency that permits the natural color of the tooth to diffusely show through the bracket. An improved translucent polycrystalline ceramic bracket having a metallic archwire slot liner to enhance sliding movement of the bracket on the archwire is described in pending U.S. applications Ser. Nos. 08/061,215 and 08/061,164, both of which were filed on May 13, 1993.
In the past, orthodontic brackets were commonly secured to bands that were placed around the teeth. Today, orthodontic brackets are often bonded directly to the surface of the teeth. Once treatment has been completed, the archwire is removed from the slot of the brackets and each bracket is then removed from the associated tooth.
Metal brackets are typically debonded by using a peeling or prying motion. U.S. Pat. Nos. 3,986,265 and 4,248,587 describe plier-type hand instruments that are used with a prying action to remove orthodontic brackets. U.S. Pat. No. 4,553,932, assigned to the assignee of the present invention, describes an peeling-type debonding tool having a pull wire with a loop for hooking a wing of the bracket and applying a pulling force to a tiewing located on one side of the bracket while a pair of spaced apart abutments engage the tooth on opposite sides of the bracket.
Peeling-type debonding methods are usually considered satisfactory for detaching brackets made of ductile materials such as metal. Debonding of such brackets often begins by fracturing the adhesive bond along one side of the bracket base, and then peeling or bending the base of the bracket so that the fracture propagates to remaining regions of the adhesive bond. In this manner, the debonding force is applied only to a relatively small, generally linear area at any particular point in time.
However, ceramic orthodontic brackets are relatively hard and brittle, and do not bend or flex like metal brackets during debonding. As a result, debonding occurs by fracturing the adhesive bond in all areas at essentially the same time, rather than in a propagating type of fracture as occurs when metal brackets are debonded by a peeling-type motion. Pulling on the tiewings of a ceramic bracket is not normally recommended because the ceramic material is brittle and the tiewings may break from remaining portions of the bracket.
Damage to the tooth structure may result during a debonding operation when excessive stress is applied to the tooth during attempts to lift or pry the bracket from the tooth. Tooth damage is more likely to occur when the tooth structure is weakened or has been previously damaged; however, such weakened or previously damaged tooth structure often cannot be noted by visual observation. Consequently, it is desirable that brackets are removed from the teeth with as little force as possible to minimize the risk of damage to the tooth.
It has been proposed in the past to weaken the strength of the bond between a ceramic bracket and the tooth so that debonding of the bracket is facilitated. However, such a solution is not entirely satisfactory because of the resulting increased likelihood that the bracket may unintentionally, prematurely debond during treatment. For example, a relatively weak adhesive may not have sufficient strength to resist debonding the bracket when the bracket is subjected to relatively large forces, as when the patient bites into a relatively hard food object. In other instances, a bracket may debond from forces exerted by the archwire or orthodontic auxiliaries or attachments coupled to the bracket. Premature debonding of orthodontic brackets represents a nuisance to both the orthodontist and the patient that is best avoided, since the detached bracket is normally re-bonded or replaced with a new bracket to finish treatment.
There is a need in the art for a ceramic bracket that provides the aesthetic advantages of ceramic material and functions similar to a metal bracket insofar as sliding mechanics are concerned, and yet is relatively easy to debond from the tooth surface. There is also a need in the art for a new method of debonding ceramic orthodontic brackets, and a hand instrument that facilitates debonding of such brackets.